Terahertz (THz) - Frequency Differential-Absorption Spectrometer for Remote Biological Agent Detection

We propose to develop a continuous wave terahertz imaging spectrometer tunable from 0.2 to 3 THz in order to remotely detect, monitor and identify chemical and biological agents such as the aerosol simulant Bacillus subtillus. The fully realized systemwill consist of a high brightness THz source illuminating the region of interest and detected by a tunable THz interferometric imaging array. The array elements will consist of a multiple spaced THz semiconductor heterodyne photomixers driven by acommon fiber optic coupled frequency stabilized tunable optical heterodyne source. In phase I, the THz imaging array with wide field of view and high spatial resolution will be designed. A proof of principle array will be constructed using modifiedcommercial THz photomixing modules driven by a single two-color diode laser optical heterodyne source. Initial tests will be made using homodyne photomixing detection. The high speed photomixing devices for heterodyne detection will be tested in orderto determine the optimum intermediate frequency. While photomixing devices will serve both as source and detectors in Phase I, the heterodyne detected array will be source independent and the optimum high power source will be chosen for Phase II. Adatabase of required THz-frequency spectral signatures for target agents and expected interferent agents will be developed using existing time-domain THz spectroscopy equipment. A successful Phase II will result in a compact tunable THz chemical andbiological agent remote detection system. No such interferometric imaging THz spectrometer is currently commercially available. The proposed system will be useful not only in defense applications as a stationary perimeter defense system and outwardlooking remote surveillance system, but for civilian security applications as well, such as airport screening for explosives, biological agents, and other contraband. In addition, the components designed will have commercial applications manufacturing,process control, medical, and environmental diagnostics.